This invention relates to heat pump systems and more particularly to a filter-dryer unit capable of operation in the unidirectional fluid line at the output of a compressor in any system utilizing refrigerant fluid.
It is conventional in most refrigeration systems to utilize a filter-dryer in the system for filtering particles of solid foreign matter from the fluid and for adsorbing water, acids and other impurities. The solid contaminants might occur as casting sand, copper oxide and metal fine from manufacturing and assembly procedures as well as from wear during operation while chemical reactions within the system may form sludges and varnishes which plug orifices within the system or attack some of the components thereof.
It is well known to remove or control the quantity of such contaminants within the system in order to avoid excessive system failures. Further it is known to utilize a filter-dryer as a preventative maintenance tool whereby an initial clean-up of a newly installed system may be performed to remove manufacturing contaminants and those introduced at the time of assembly of the system and yet the filter-dryer can still be effective over the lifetime of operation of the system to maintain it in a high degree of cleanliness.
The filter-dryer is typically installed in the liquid line of a refrigeration system in order to avoid the high pressure drop which would result if the unit were installed in the portion of the system in which the refrigerant is in a vapor state. Pressure drop anywhere in the system reduces the refrigeration capacity, thereby increasing the energy requirements to cool a given load. Recently, the heat pump system has become very popular in the interests of energy conservation, such system acting as a reversible refrigerant system serving as an air conditioner during the summer months and as a heater during the cooler months. A heat pump system is effected by switching the direction of refrigerant flow in the liquid lines so that the role of the evaporator and the condenser are reversed. However, if a liquid line dryer is used in such a system, it would result in a condition of flow reversals in the dryer itself with a release of the contaminants trapped therein into the system. Many attempts have been made in order to accommodate such conditions including the use of dual liquid line dryers and check valves in order to route the flow of refrigerant in a unidirectional manner through each filter-dryer unit. Such installation however is costly due to the additional plumbing required and increases the probability of increased failures due solely to the additional number of components involved.
This problem could be avoided in the heat pump system by the introduction of the filter-dryer in either the discharge or suction line of the compressor where only unidirectional flow of fluid occurs. Suction line filter-dryers are in use but have been determined as not so desirable since they introduce a large pressure drop in this low refrigerant density fluid line, and the energy penalty is considerable. In the past the discharge line location has not been considered practical because of the relatively high temperature levels involved, which affects primarily the water retention capability of the desiccant within the filter-dryer unit. A filter-dryer located in the discharge line of the compressor, however would not result in such great energy penalty due to the relatively higher density of refrigerant in this line and could provide a significant cost advantage to the customer in avoiding the requirement for redundant liquid line units and accompanying switching devices.
U.S. Pat. No. 4,104,044 discloses one prior art solution to the use of filter-dryer assemblies in the heat pump system, using dual filter-dryers having internal check valves, the units being in parallel connection with dual expansion devices, and all components located in the liquid lines of the system.
U.S. Pat. No. 3,783,629 discloses one example of the use of a filter-dryer at the discharge side of the compressor. In this non-reversible refrigeration system, hot exhaust gas from the compressor is delivered initially to an enlarged pipe forming part of a jet ejector across which the filter-dryer is connected. It is stated that the combination of ejector and filter-dryer in this arrangement alleviates the problem of pressure drop in the system introduced solely by a filter-dryer, however it is apparent that only a portion of the refrigerant passes through the dryer unit in this bypass type system. Further, the filter-dryer is located a considerable distance from the outlet of the compressor being connected by means of the enlarged pipe and a further conduit, significantly also introducing cooling fins on the filter-dryer unit to allow the return of liquid to the downstream side of the jet ejector. Such type of system is apparently feasible only where there is adequate space available for such piping components and the large size filter-dryer unit indicated.
U.S. Pat. No. 3,175,342 depicts a filter-dryer unit in the discharge line of a compressor, stating that a conventional device may be so employed. In fact, this patent relates to the introduction of a clean-up filter in the suction line of the compressor as a temporary device when a new compressor or the like is installed in the system and suggests otherwise that a filter-dryer would be employed in the liquid lines of such system. It was conventional at that time to employ filter-dryers in the liquid line portion of the system and it is believed that the filter-dryers that were state-of-art as of the time of issuance of the patent would not have been suggested nor practical for application in the discharge line of a compressor in a refrigerating or heat pump system. This patent does not state that molecular sieve could be used as the desiccant in a discharge line dryer which would likely be necessary in order to have an operable unit and it is believed that the showing of a filter-dryer in the discharge line was inadvertent.